Parks Coppell ABQ-CS 861022 ANDERSON ENGINEERS, INC.
LA, ND & WATER ~-NGINEE,~',
October 22, 1986 13740 Midwoy Rood · Suite 508~=e ~!Ios Texas 75244 ~~ 214-960 0977
~. 3chh C. Karls~uher, PE
16135 P,eston Rood, Suite 112 '~' ,,';. /'/?
Dallas, Texa~ 752~8 "/ /~/
Lakes for Tk~ Park~ of
Dear Mr. Karlsruher:
A review and onoiyses of the proposed outIet drains for the Iokes in
The Porks of Coppell have been compieted. The review of the
hydrouIics of these structures has been based upon the pIons by
Threodgill-Dowdy and Associates received from your office by way of
tronsmittoi doted October 18, lg88.
The onoiysis of each of the outiet drains was based upon the 2- and 5-
yr storm events. Representative hydrogrophs for each of the
contributing drainage areas were generated by use of HEC-1 and routed
through the respective iokes, based upon ovoiIobie storage voiume
described os o stage versus oreo relationship determined from the
pions. A stage versus discharge reIotionship was formulated for each
outlet structure based upon the details contained in the submitted
plans and assuming o free outfoll condition. For each lake-outlet
drain combination, the 2-, 3-, G-, 12- and 24-hr storm durations were
analyzed to determine the critlcol condition, 1.e., the storm event
that resulted in the greatest peak discharge.
The moxlmum water surface elevation wlthln the lake for the crlticol
storm event was then compared to the tollwoter conditions for the
outlet structure into Denton Creek. The tollwoter conditions were
based upon the results of the previous Denton Creek Floodplain Study
by Anderson Engineers, Irc., ossumlng occurrence of the histor£c 2-
and 5-yr frequency peak discharges within a post-construction channel
for Denton Creek. The maximum water surface elevation within each
lake was also checked wlth the proposed rlm elevation to determine if
overtopping occurred. A summary for each of the lakes follows. The
numbering system corresponds to the drain designation within the
construction plans.
REGISTERED ALABAMA ARKANSAS COLORADO iLLINOIS LOUISIANA MISSOURI NEW MEXICO TEXAS
LAKE #1
Storm Frequency (¥rs) Peak O (cfs} Lake Max WS E[ev Tai[water
2 29 448.75 444.92
5 40 449.~9 449.89
LAKE #2
Storm Frequency (yrs) Peak O (cfs) Lake Max WS E[ev Tai~water
2 27 448.66 444.58
5 $8 448.99 449.65
LAKE #3
Storm Frequency (yrs) Peak Q (c~s) Lake Max WS Elev Toilwoter
2 77 449.61 445.98
5 95 450.64 449.18
LAKE ~4
Storm Frequency (yrs) Peak Q (c~s) Lake Max WS Elev Tailwater
2 57 449.38 447.25
5 66 449.93 448.16
LAKE #5
Storm FreQuency (vrs) Peak O (c~s) Lake Max WS Elev Tailwater
2 61 447.25 443.56
5 78 448.16 448.78
2
The peak discharges given in the previous tables correspond to outflow
from the drains assuming a free outfall condition. The critical storm
from which these peaks ore produced correspond to a 12-hr storm
duration for Lakes #1, #2 and #4. The 24-hr storm duration was found
to be critical for Lakes #3 and #5. By inspection of the maximum
water surface elevation in the lake relative to the tailwoter
elevation in Denton Creek, it appears that positive outflow from Lakes
#1, #2 and #5 will not be possible in the 5-yr storm event.
All of the lakes appear to contain the runoff volumes generated in the
two storm events onolvzed, with the exception of Lake #3. /he rim
elevation for this lake was determined to be approximately 45~ from
the proposed construction plans. The lake maximum water surface
elevation is given in the previous table as 450.6~ for the 5-yr storm
event, thus overtopping by ~.64 ft. Inspection of the stage
hydrograph for the lake indicates a duration of approximately 9 hfs
for which the water surface elevation is greater than ~5~.
/he summary of our review contained herein hopefully is sufficient for
your purposes. Should you have any questions or require further
detail, please advise.
Sincerely,
ANDERSON ENGINEERS, INC.
Mark D. Walter, ET, EIT
Staff Englneer